The present disclosure relates to disk brake pistons and piston systems, such as are used for various vehicles including automobiles, trucks, aircraft, trains and the like. Embodiments of the disclosure include pistons having provision for a screw actuated braking capability including those having a treaded actuator system for a parking brake and a pressure actuated capability for additional braking capability such as braking capability actuated by a pneumatic or hydraulic pressure source. In various embodiments, the screw actuated braking capability can be actuated by a lever or a motor such as an electric motor or any other suitable type of motor. In some embodiments, a device, such as a lever or other device such as is used for setting and releasing a parking brake can be used to rotate the spindle 3.
Disk brake pistons, such as disclosed herein, can be of any suitable construction, and can be of any suitable material or combination of materials to provide the desired strength, durability and responsiveness. Features such as low weight and low internal volume can be desirable.
As shown in FIGS. 1 and 2, an embodiment of a forged steel piston 1 can have an internal cavity 2 with a threaded spindle 3 engaging an internally threaded nut 4 and a nut contact surface 9 having a conical shape which interfaces with a piston contact surface 10 of the nut 4. Upon relative rotation between the spindle 3 and the nut 4 the nut moves linearly toward or away from the brake pad end of the piston 5. Upon relative rotation in a first direction, the nut 4 moves toward the brake pad end of the piston 5 and then engages and pushes against the brake pad end of the piston, with the brake pad end of the piston 5 engaging the brake pad 6 directly or indirectly and causing a braking action between the brake pads 6, 7 and the rotor. In some embodiments, the movement of the nut 4 toward the brake pad end of the piston 5 can be done in conjunction with a pressure force being applied to the piston, and the force applied by the nut 4 to the brake pad end of the piston 5 can supplement the pressure force or can serve to partially or fully maintain the force applied to the piston by the pressure system when the pressure is reduced or eliminated. In some embodiments, the spindle 3 and nut 4 can be part of a parking brake, such as an electromechanically actuated parking brake actuated by a motor 8.
Upon relative rotation in a second direction, the nut 4 moves away from the brake pad end of the piston 5 and reduces and/or removes the force of the nut 4 acting upon the brake pad end of the piston 5.
However, while pistons made from forged steel with machined surfaces can be strong and have precise dimensions, they can be heavy and expensive to make. Difficulties in manufacturing can be particularly evident in some aspects of the machining necessary for the internal structure of the piston.
FIG. 3 shows a brake system 210 having a piston partially constructed of phenolic material. Here, the brake system 210 may also include a first brake member 222 that is used in engaging a first side 224 of the wheel brake rotor 220 and that is attached to the first portion 214 of the brake caliper housing 212. Similarly, the brake system 210 may include a second brake member 226 that is used in engaging a second side 228 of the wheel brake rotor 220 and that is attached to the second portion 216 of the brake caliper housing 212. Each brake member 222, 226 includes a brake pad 230 having a brake shoe 232 attached thereon.
With reference to FIG. 3, the brake piston 270 may include a core 274 having an axial height H1 and an outer layer 276 having an axial height H2. As shown, H2 is at least 0.5H1. The opening 272 may be formed in the core 274, as shown. The core 274 may be formed substantially of a metal and the outer layer 276 may be formed substantially of phenolic material. In one embodiment, the core 274 is formed substantially of steel and the phenolic outer layer 276 is attached to the core 274 in a process known as overmolding. In one embodiment, at least one surface variation 277 is formed on an outer surface of the core 274 to improve retention of the outer layer 276 to the core 274 during the overmolding process. By surface variation it is meant a change on the surface that is either concave or convex with respect to the surrounding surface.
A caliper piston seal 280 may be positioned between the brake caliper housing surface defining the bore 234 and the outer layer 276 to maintain proper closure around the piston 270. With reference now to FIG. 3, the brake piston 270 may have a first end 282 with a brake member contact or mating surface 284 that contacts the second brake member 226 to cause it to engage or contact the second side 228 of the wheel brake rotor 220. In one embodiment, the brake member contact surface 284 is located on an outer surface of the metal core 274 that has no outer layer 276. Thus, the brake member contact surface 284 in this embodiment has no phenolic material improving the mating engagement of the brake piston 270 to the brake member 226. The opening 272 in the core 274 may be defined by a surface that includes a first spindle nut contact surface 286 that is contacted by a first outer surface 251 of the spindle nut 252 to prevent rotation of the spindle nut 252 with respect to the brake piston 270. The opening 272 in the core 274 may also be defined by a second spindle nut contact surface 288 that is contacted by a second outer surface 253 of the spindle nut 252 to force the brake piston 270 to slide within the bore 234. In one embodiment, the second spindle nut contact surface 288 is angled, as shown, to provide a better surface for the spindle nut 252 to act upon. In one embodiment, neither the first nor the second spindle nut contact surfaces 286, 288 has a phenolic material thereon improving the mating engagement of the spindle nut 252 to the brake piston 270.
Other configurations can be used such as that shown in FIG. 4 which shows a disc brake caliper assembly 310 having a rod 340 positioned within the piston 324. In some situations, severe operating conditions may force piston 324 into bore 322 to a knock-back position, K, resulting in an undesirable clearance, C. On the next brake application, the operator will have to depress the brake pedal much farther than desired to fill chamber 326 with sufficient fluid to apply the brakes. To prevent piston 324 from being forced from the normal retracted position, R, to the knock back position, K, the present invention incorporates a linkage 336. Linkage 336, preferably a shaft with a threaded end 338, is arranged adjacent to piston 324 and movable between first, F, and second, S, positions. Specifically, a rod 340 is integrally formed with piston 324 and extends therefrom toward end 338. A support 342 is secured to housing 318 within bore 322 for supporting linkage 336. Support 342 has a hole 344 for at least partially receiving rod 340 and a threaded portion 346 for threadingly receiving end 338 of linkage 336.
As brake pads 312 wear, a clearance will result between rod 340 and linkage 336 that corresponds to the clearance, C, between the normal retracted position, R, and the knock-back position, K. The clearance between rod 340 and linkage 336 defines first position, F, of linkage 336. While linkage 336 is in the first position, F, piston 324 is able to move to the knock-back position, K, in the same undesirable manner as the prior art.
An actuator 350 is used to rotatingly drive linkage 336 to eliminate the clearance between rod 340 and linkage 336 by moving linkage 336 from the first position, F, to the second position, S. In the second position, linkage 336 abuts rod 340. Since linkage 336 is supported by support 342, which is secured to housing 318, rod 340 is prevented from moving inwardly relative to housing 318. In this manner, actuator 350 eliminates the clearance to prevent piston 324 from moving within bore 322 away from rotor 314 from the normal retracted position, R, to the knock-back position, K, in response to severe operating conditions.
Further, while the use of plastic material, such as those made from phenolic resin, for production of pistons can result in a lighter and less expensive piston, a plastic piston is generally not as strong as steel and can be prone to catastrophic failure such as cracking.
Accordingly, it is desirable to make a piston which is lighter weight and yet sufficiently strong and tough to survive the forces associated with braking a vehicle to slow, stop or maintain the position of the vehicle.
In addition, the construction of a disk brake piston, a disk brake piston assembly and the features internal thereto are desirably designed so as to facilitate assembly and service operations, including but not limited to filling the brakes with an appropriate fluid and purging undesirable fluids from the interior of the piston, such as by bleeding a hydraulic brake system.